Window not showing up using show()

I have some code for opening a window from the main one, but it doesn't work. "Window open." gets printed, then nothing else happens, it's just as if show() didn't do anything. This is invoked from a menu using a connector and an action.

@Wieland thank you. I have tried it and it is an excellent answer, but I don't still get the clue. I have added a 1sec delay to the function after calling show() to see if the windows appears, no luck. I have made the changes you have proposed, and I now have the following code:

Parents are important for stacking order and focus management. What's more is in your code you're not deleting it explicitly, so if you don't give it a parent it will leak.
Better than not giving it a parent would be to either use QDialog instead or make it a window via a flag, i.e.: